The sad death, last month, of Sir Gerald Kaufman means that, hot on the heel the 1-all defeat of Labour in Copeland and Stoke-on-Trent, another by-election looms, most likely on May 4.

Manchester Gorton, Sir Gerald’s seat, was formed in 1916 and, since then, Labour have old failed to hold it once – in the 1931 general election, following Ramsey MacDonald’s Labour government collapse in the face of the great depression.

In the 2015 general election Labour took 67% of the vote, giving them a majority slightly over 24,000; their 13th safest seat by majority, and the 15th by vote share. The Conservatives, UKIP and the Lib Dems combined didn’t even reach 10,000 votes.

As by-elections go this should be one equivalent to an FA Cup qualifier between Manchester United and some no-league side whose striker is 63 and whose goal-keeper is off his narcolepsy meds. The problem with those, of course, is that unless Manchester drive home a 30-nil victory it looks like their hearts weren’t really in it.

This is Corbyn’s problem…OK, sorry, it’s Corbyn’s problem for this particular by-election; he has many other problems beyond it. It may be inconceivable that he could lead Labour into defeat at Gorton, but he could fail to win convincingly and find that just as damaging.

In 2015 the (distant) runners-up to Labour were the Greens, taking just shy of 10% of the vote. If the mating call of the Corbynite, “people had stopped voting Labour because it wasn’t left-wing enough”, is true then that 10% of the electorate should now be rushing to vote for Corbyn’s Labour. The party should be looking for a repeat of their by-election success in Oldham West and Royton in December 2015.

Just a few miles away from Gorton, Oldham was the first by-election test of Corbyn’s leadership, and saw the party increase their vote share by 7 percentage points. Nobody really expects that to happen, of course. The political landscape has shifted quite a lot in the past 15 months; Britain has voted to Brexit, May has taken the Conservatives rightwards, UKIP appear to be a spent force, and Labour have slumped in the polls. Corbyn himself has gone from being the unknown newcomer, promising to inspire millions to return to Labour, to being the most unpopular Labour leader since polls began, presiding over a party in turmoil.

A straightforward application of current polling data would see Labour slipping by 7 points with, assuming a turnout of about 80% that at the general election, their majority falling to around half of its current level.

This is bad, but not necessarily catastrophic. However, their are two other factors in play.

Unlike Copeland, where Labour were able to spin a ‘Labour’s vote share has been slipping for years’ story (by using 1997 as the baseline, rather than the high-point), the 2015 election saw Labour’s vote share increase by 17 points. This was mainly at the expense of the Lib Dems, whose own share fell by an incredible 28 points, as voters punished them for the actions of the coalition government. Like most large cities, Manchester supported remaining in the EU, by 60% to 40%. With Labour now backing Brexit, and actively helping the government get the Brexit bill through parliament, we might see a lot of those erstwhile Liberals returning to their party.

At the other end of the spectrum, it’s uncertain what UKIP will do. The party is tearing itself apart, its leader was disgraced in the Stoke-on-Trent by-election, and they know they have nothing to gain by throwing everything at a remain-supporting Labour stronghold. A couple of thousand UKIP voters with no-candidate, or a very low-profile one, may be gift to the Tories, possibly even pushing Labour’s majority below the 10,000 mark.

A perfect storm of a strong Liberal Democrat candidate with a weak or no-show UKIP one might even see Labour’s majority reduced to just a couple of thousand. Where Corbyn to come so close to losing such a safe seat it would, surely, be a blow beyond spinning and the final nail in his coffin.